Geomagnetic Activity and Airglow

Taking starscape photos last week I was surprised at the intense red glow appearing in the photographs. All across the southern sky were glowing areas of sky, here and there dark rifts cut through the glow. Set beside the Winter Milky Way it created beautiful photographs.

Airglow or auroral glow?
Airglow or auroral glow? An odd red glow in the photos during a strong geomagnetic storm.
The airglow was intense enough to be visually seen when I stepped away from the camera and let my eyes adapt to the darkness. Away from the Milky Way, in what should be dark sky, a faint red glow pervaded. I wondered what was going on, the normal airglow over Mauna Kea is quite faint and usually very green.

I was even further surprised when I later found out that a strong geomagnetic storm was in progress that night. Kp=6 conditions from back to back CME’s were creating strong aurora over Canada and the upper US.

Was I seeing some sort of auroral glow? In Hawaii? At 20°N latitude? This did not seem likely, but something unusual was occurring!

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Tracking the Aurora Borealis

As our Sun continues through the current solar maximum we should have plenty of opportunities to view one of the most sublime of all natural spectacles, the Aurora Borealis.

Aurora Borealis
A strong auroral display over St. Johns Harbor, Alaska on the evening of September 4, 2012
While traveling in Alaska and other northern regions there is always a possibility of a good showing. To make the most of the opportunity a little information cane be useful…

Solar Activity

Solar activity waxes and wanes in an eleven year cycle. When active there are increased numbers of sunspots and solar flares. It is this activity that can have such a dramatic effect here on Earth. A strong solar flare can be accompanied by a release of enormous quantities of material from the Sun. Called a coronal mass ejection (CME) this material streams outwards from the Sun. If the Earth happens to be in the path this material will strike the Earth’s magnetic field, causing the field to distort and reverberate with the impact. Charged particles are channeled into the atmosphere along the magnetic field to create a glowing spectacle.

Our current solar maximum should run through 2013 and into 2014 providing excellent auroral viewing conditions for the next year or two.

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Aurora Borealis

This trip to Alaska offered an opportunity that I had not experienced on previous trips due to the confluence of two conditions… I would be visiting later in the year than usual, it would actually get properly dark. When visiting Southeast Alaska in June and July the amount of darkness is dramatically limited by long summer days. The second condition is even less easily arranged… Our Sun is near the peak of its eleven year solar cycle. This results in more solar activity including large sunspots and energetic solar flares.

Put the two of these factors together and there is a good possibility of seeing the Aurora Borealis.

It is only a possibility, not a certainty by any measure… This was not a trip to the far north, where the auroral circle usual sits. If one were to travel north of Fairbanks into the true arctic one is almost guaranteed to see the aurora during solar max. I would be traveling between Juneau and Anacortes, from 58 to 48 degrees north latitude. At these latitudes it would take a strong geomagnetic storm to bring the aurora south into view. The chances of such a strong storm were relatively good, we are currently experiencing an active Sun near solar maximum, averaging a decent storm every month or two. In any case the odds were a bit better than seeing the aurora at home in Hawai’i.

At least there would be no light pollution to deal with, significant outposts of civilization are sparse along the route we would be traveling. One complication would be weather… Of the twenty days I would spend in northerly latitudes, about half were clouded over, thus the odds of seeing a good auroral display were modest, maybe even unlikely.

We got lucky.

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Geomagnetic Update

The CME from yesterday’s solar flare struck at about 01:00HST, not as strongly as predicted. Right now there is a geomagnetic storm going on, but only at a moderate intensity, Kp=5. It takes something with a Kp>10 before aurora become a likelihood at low latitudes. Expect some nice photos from the folks up north as they get to enjoy the show.

The sunspot responsible for the flare, AR1429, is still there, pointed directly at our Earth. It harbors the energy for more X class flares, stay tuned!

Sun at 304nm
The Sun at 30.4nm (extreme ultraviolet) on 8Mar2012 showing the large sunspot group AR1429 (upper center), image credit NASA/SDO

Geomagnetic Storm Warning

At 00:28UT March 7th (14:28HST March 6th) our Sun let loose with a X5-class solar flare. This is the largest event in many years, and the impact will be felt here on Earth later today. We can expect a major geomagnetic storm when the mass of charged particles strikes the Earth’s magnetic field sometime around 0625UT (±7hr) on March 8th (2025HST March 7th).

Skywatchers at all latitudes have a chance of seeing aurora.

Yes, this means a chance of seeing aurora here in Hawai’i. I have seen aurora in southerly locations, including Tucson at 32° latitude. It is possible given a strong enough event. Fortunately the tropical storm we have experienced for the last few days appears to be clearing out. I will have to check the northern skies this evening.

The culprit is sunspot group AR1429, an enormous magnetic disturbance on the face of the Sun. An enormous amount of energy stored in the twisted magnetic fields of AR1429 was released when the fields ruptured. The result was a powerful solar flare. This event was recorded by several spacecraft at a number of wavelengths. The resulting imagery and movies are worth checking out.

For updated info on the event you can check in with dedicated solar monitoring websites like SpaceWeather or the NOAA Space Weather Prediction Center